Low back pain and radiculopathy as a result of herniated intervertebral disc represents a major health problem in the United States and all over the world. About 300,000 Americans and about the same number of people throughout the world outside the USA are operated upon each year due to this problem. Even many more people might benefit from surgical help, as those that undergo the surgery represent only about 20% of those with cervical pathology referable to the intervertebral disc.
An intervertebral disc is a structure that occupies the space between the vertebrae. It serves, in particular, as a load-absorbing cushion.
FIG. 1 is a cross-sectional view of a vertebral column through a healthy intervertebral disc 20, and FIG. 2 is a side view on a part of the vertebral column illustrating the position of the disc 20. As can be seen from FIGS. 1 and 2, the disc 20 consists of two parts: a ring-like external part 22, known as “annulus” (or “annulus fibrosis”), and an internal, central part 24, known as “nucleus” (or “nucleus pulposus”). The tissue of the annulus 22 degenerates with age or as a result of some injuries, or illnesses. When annulus 22 degenerates, its fibers weaken, and external forces applied to the adjacent vertebrae, can cause the rupture of the annulus fibers and nucleus tissue protrusion, shown in FIGS. 3 and 4 that correspond respectively to FIGS. 1 and 2. This creates a disc herniation 26 (FIG. 3), which, in turn, may cause a pressure on the adjacent nerve root 28 (FIGS. 1 and 3), resulting in pain.
It is understood that herniation may occur in any other part of the disc and cause different symptoms and that the herniation position shown in FIGS. 3 and 4 is given just as an example.
At the present time, several approaches exist for treatment of the problem described above. The first method is called “laminectomy”. This is a surgical procedure, which involves accessing a symptomatic disc by excising a significant amount of the vertebral lamina, followed by removal of the herniated disc material. A laminectomy is a somewhat destructive procedure, which might cause extensive scarring and long (up to 9 days) hospitalization, with an up to 3-month postoperative recovery period.
Another approach is called “microlumbar surgery” (“microsurgical discectomy”, or “microdiscectomy”). It is similar to laminectomy in that the disc is accessed through an incision, made on the patient's back and developed into a channel to the symptomatic disc. Unlike laminectomy, the microdiscectomy employs a microscope, allowing a smaller incision (about 2 times less than during the laminectomy). This method permits the surgeon to use microsurgical tools, and avoid much of the bone dissection. This is less invasive compared to the laminectomy, though the existing microdiscectomy may still cause some complications similar to those associated with laminectomy, for example, possible injury to the nerve root and dural sac, postoperative scarring and relatively long recovery time. Furthermore, the paraspinal musculature must still be retracted out to the level of the facet for the duration of the procedure.
Other methods of treatment consist of a removal of the disc nucleus tissue either by suction or by dissolving it. The former approach (suction) is known as a percutaneous discectomy and is carried out by utilizing hollow needles of special design, which are placed through the back muscles into the center of the disc (into the nucleus area) and then allow suction of the tissue. The latter approach (dissolving) is known as chemonucleolysis, which is carried out by injecting a special enzyme (chymopapain) into the center of the disc. The chemonucleolysis may cause severe pain, spasms, and anaphylactic shock (the mortality rate associated with chemonucleolysis has been estimated at about 0.5%). Both approaches belong to so-called Minimally Invasive Spinal Surgery (hereinafter referred to as MISS) methods. As a result of removal of the disc nucleus tissue, the protruded disc material can then collapse back inside, toward the center of the disc, which can in turn, reduce the pressure on the spine nerve roots.
Many attempts have been made heretofore to improve methods and surgical instruments employed in the percutaneous discectomy procedures.
For example, U.S. Pat. No. 4,545,374 issued in 1985 to R. Jacobson discloses a method and instruments for performing a percutaneous lumbar discectomy. The method consists in accessing the lumbar region of the spinal column by laterally inserting a cannula through the patient's side above the iliac crest to contact a predetermined position in the lumbar region and passing instruments through the cannula. This method is useful for performing percutaneous lumbar discectomy by cutting a portion of the patient's disc annulus and nucleus through the cannula and removing a desired amount of nucleus material. The cannula has a tubular member and anchor means attached to one end of the member for anchoring the cannula in the body tissue to prevent shearing movement between it and the tissue. Other instruments for performing a percutaneous lumbar discectomy are disclosed, including a speculum and trocar for percutaneously inserting the cannula into the patient, a discectomy knife for cutting disc nucleus material and rongeur forceps for removing the disc material. The above instruments may be combined in a surgical apparatus.
The method of U.S. Pat. No. 4,545,374 has the following drawbacks: 1) the material is removed from the center of the disc only, thus preventing a surgeon from excising the fragments from the actual herniation site, which may or may not cause recurrent symptoms; 2) this technique is unsuitable for noncontained (or sequestered) herniations, since it does not give a surgeon access to the epidural space.
U.S. Pat. No. 5,084,043 issued in 1992 to P. Hertzmann et al. describes laser-assisted disc decompression (LDD). It utilizes a high-energy laser beam to vaporize the affected tissue instead of removing it mechanically. Like in the percutaneous approach described above, one of the disadvantages inherent in this procedure is that it deals with the disc nucleus, rather than with the herniation itself.
Several MISS methods, based upon contemporary technology achievements were introduced during last 10–15 years. For instance, U.S. Pat. No. 5,437,661 issued in 1995 to B. Rieser discloses a method for removal of prolapsed nucleus pulposus material on an intervertebral disc by using a laser. A cannula is inserted into the spinal foramen. Once the cannula has passed the ligamentum flavum, a laser fiber is inserted into it. The laser fiber contacts the prolapsed material and a laser beam substantially eliminates the prolapsed material within the spinal foramen.
Lasers are both expensive and somewhat tedious to use in these procedures. Another disadvantage with lasers is the difficulty in judging the depth of tissue ablation. Since the surgeon generally points and shoots the laser without contacting the tissue, he or she does not receive any tactile feedback to know how deeply the laser is cutting. Because healthy tissue, bones, ligaments and spinal nerves lie in the close proximity to the spinal disc, it is essential to maintain a minimum depth of tissue damage, which cannot always be ensured with a laser.
U.S. Pat. No. 6,264,650 issued in 2001 to D. Hovda et al. describes systems, apparatus and methods for ablation, resection, aspiration, collagen shrinkage and/or hemostasis of tissue and other body structures in open and endoscopic spine surgery. In particular, the invention includes a channeling technique in which small holes or channels are formed within spinal discs, and thermal energy is applied to the tissue surface immediately surrounding these holes or channels to cause thermal damage to the tissue surface, thereby stiffening the surrounding tissue structure and reducing the volume of the disc to relieve pressure on the surrounding nerves, and thereby relieving neck or back pain.
U.S. Pat. No. 6,254,553 issued in 2001 to L. Lindgren et al. offers a method and a device for non-invasive treatment of biological tissue by changing or degenerating the tissue. This device has a treatment transducer for treating intervertebral discs, preferably nucleus pulposus, by ultrasound. The ultrasonic field of the ultrasonic transducer is focused in the symptomatic intervertebral disc, preferably in nucleus pulposus of this disc, for heating the tissue to such a temperature that the tissue in the focal area degenerates, whereby the pressure in the intervertebral disc and thus, the pressure against the spinal nerve roots is reduced.
Both methods described in U.S. Pat. No. 6,264,650 and in U.S. Pat. No. 6,254,553 make it complicated for a surgeon to focus treatment on the symptomatic site, without affecting the surrounding tissues.
Single-portal MISS methods are limited to the use of one channel at a time. It was suggested to introduce a second portal to the annulus as described by Shreiber et al. in Clinical Orthopaedics and Related Research No. 238. However, this biportal procedure assumes the second portal to be created from the opposite side to the first portal (bilateral), hence increasing the operating time, post-operative morbidity, surgeon exposure to radiation. It may also cause excessive removal of disc nuclear tissue, therefore increasing the possible post-operative stenosis (narrowing) of the foramen.
Therefore, there is a need for a unilateral multiportal approach for the percutaneous disc procedures. Such attempts were made by either using an oval cannula, which allows using several tools at a time (see U.S. Pat. No. 6,228,022 issued on May 8, 2001 to T. Friesem et al, and U.S. Pat. No. 5,762,629 issued on Jun. 9, 1998 to P. Kambin), or introducing a second cannula for a biportal unilateral approach (the U.S. Pat. No. 5,762,629 and U.S. Pat. No. 5,730,754 issued on Mar. 24, 1998 to T. Obenchain). These approaches do not provide a comprehensive solution for percutaneous disc surgery. Oval cannulae, though providing additional space for instruments, are still too restrictive, while more invasive than circular ones. The method described in U.S. Pat. No. 5,730,754 still needs accurate targeting and it is not sufficiently universal. U.S. Pat. No. 5,762,629 allows inserting a second cannula using a special targeting device, but has following disadvantages: 1) the targeting device is rigid and does not allow the flexibility required by a surgeon for the formation of an angle between inserted cannulae; 2) after cannulae are inserted, the targeting device is removed, leaving the cannulae completely unlinked, so that a surgeon cannot keep them interrelated. In case the position of one of the inserted cannulae should be temporarily changed, it becomes a problem to reorient them, especially when more than two cannulae are used for the surgery.
Another common disadvantage of the existing devices for the percutaneous surgery is that they require the operation to be carried out under X-ray monitoring at all steps of the surgery, i.e., during insertion of each additional cannula and occasionally during the procedure itself. Simultaneously used cannulae are not interrelated with regard to their relative movements, once a cannula is shifted from its original position aligned under X-ray or by means of a special guiding device, it cannot be returned back to the original position, unless X-ray is used again. Such multiple X-ray monitoring subjects both the surgeon and the patient to an increased doze of radiation.